TPUs (thermoplastic polyurethanes) are currently being used in manufacturing a wide variety of products for many applications by various melt processing techniques, such as injection molding and extrusion. For instance, TPUs are commonly used in making seals, gaskets, catheters, wires and cables. Such TPUs are typically made by reacting (1) a hydroxyl terminated polyether or hydroxyl terminated polyester, (2) a chain extender, and (3) an isocyanate compound. Various types of compounds for each of the three reactants are disclosed in the literature. Such TPUs are segmented polymers having soft segments and hard segments. This feature accounts for their excellent elastic properties. The soft segments are derived from the hydroxyl terminated polyether, polyester, polycarbonate, or polycaprolactone and the hard segments are derived from the isocyanate and the chain extender. The chain extender is typically one of a variety of glycols, such as 1,4-butanediol. For instance, U.S. Pat. No. 5,959,059 discloses a TPU made from a hydroxyl terminated polyether, a glycol chain extender, and a diisocyanate. This TPU is described as being useful for making fibers, golf ball cores, recreational wheels, and other uses.
In many applications, it is desirable or even critical for the TPU utilized in manufacturing articles to exhibit good chemical resistance, dimensional stability, set properties, heat resistance, oxidative resistance, and creep resistance. These physical and chemical characteristics are important in articles that are exposed to chemicals, solvents, and/or elevated temperatures. For instance, it is normally important for seals, gaskets, wires and cables that are used in industrial applications to possess these desirable characteristics. This is particularly the case in under-the-hood automotive applications where the part made with the TPU may well be exposed to elevated temperatures and organic liquids, such as gasoline and motor oil. For example, spark plug wires and other wires used in automotive applications need to be both oil and heat resistant. Seals and gaskets used in internal combustion engines, heavy equipment, appliances, and countless other applications also need to be resistant to heat and solvents.
Crosslinking a thermoplastic polymer into a thermoset network is one known technique for improving chemical resistance, dimensional stability, set properties, heat resistance, oxidative resistance, and creep resistance. However, thermoset resins cannot be processed using standard melt processing techniques, such as injection molding, blow molding, and extrusion. In general, thermosets are molded into the desired form and cured into the shape of the mold via a more labor intensive, time consuming, and expensive curing technique. Additionally, defective thermoset parts and scrap cannot be recycled and remolded like thermoplastics. This leads to polymer waste which also adds to total cost and has a detrimental environmental impact.
There is a need for a TPU that can be melt processed into a desired shape by injection molding, blow molding, extrusion, or the like, and then crosslinked into a thermoset network. It is, of course, important for the thermoset network to exhibit good chemical, solvent, and heat resistance which is characterized by good dimensional stability, set properties, oxidative resistance, and creep resistance. Such a TPU could beneficially be used in manufacturing a wide array of component parts and articles of manufacture having improved chemical and physical characteristics. For instance, such a polymer could be advantageously utilized in manufacturing seals, gaskets, wires, cables, hoses, pipes, tubes, and other industrial and consumer products that have improved chemical, solvent, and heat resistance. There is, accordingly, a need for a TPU composition that can be molded into useful articles like a thermoplastic but which has the desirable physical and chemical properties of a thermoset TPU.